Electroluminescence devices which utilize the electroluminescence show high self-distinguishability because of the self-emission and are excellent in impact resistance because they are completely solid devices. Therefore, electroluminescence devices have been attracting attention for application as light emitting devices in various types of display apparatus.
The electroluminescence devices include inorganic electroluminescence devices in which an inorganic compound is used as the light emitting material, and organic electroluminescence devices in which an organic compound is used as the light emitting material. Organic electroluminescence devices have been extensively studied for practical application as a display device of the next generation because the applied voltage can be decreased to a large extent.
As for the construction of the organic electroluminescence device, the basic construction comprises an anode/a light emitting layer/a cathode. (This description shows that an anode, a light emitting layer, and a cathode are laminated in this order. Other constructions are described in the same manner.) Constructions having a hole injecting and transporting layer or an electron injecting and transporting layer suitably added to the basic construction are known. Examples of such construction include the construction of an anode/a hole injecting and transporting layer/a light emitting layer/a cathode and the construction of an anode/a hole injecting and transporting layer/a light emitting layer/an electron injecting and transporting layer/a cathode. The hole injecting and transporting layer has the function of transporting holes injected from the anode to the light emitting layer. The electron injecting and transporting layer has the function of transporting electrons injected from the cathode to the light emitting layer. It has been known that, when the hole injecting and transporting layer is inserted between the light emitting layer and the anode, more holes are injected into the light emitting layer in a lower electric field, and electrons injected into the light emitting layer from the cathode or the electron injecting and transporting layer are accumulated at the interface between the hole injecting and transporting layer and the light emitting layer because the hole injecting and transporting layer does not transport electrons. As the result, efficiency of the light emission is increased.
Organic electroluminescence devices have a problem that, because an ultra-thin film made of an organic compound is used in organic electroluminescence devices, the thin film is crystallized to cause dielectric breakdown after storage of the devices for a long time.
Heretofore, in organic electroluminescence devices, a phthalocyanine material is generally used at the interface with an anode as the hole injecting material. The phthalocyanine material is a particularly easily crystallizable material among organic materials used in electroluminescence devices, and development of a hole injecting material which can replace the phthalocyanine material and shows a high degree of amorphous property has been desired.
To solve the above problem, a technology using an amine of the dendrimer type as the hole injecting material which can suppress the dielectric breakdown in the device has been proposed (the specification of Japanese Patent Application Laid-Open No. Heisei 4(1992)-308688). However, this technology has a problem that the efficiency of light emission of the obtained device is low. A technology using an organic semiconductor of the oligomer type as the hole injecting material has also been disclosed (the specification of European Patent No. 439627). However, this technology is not suitable for practical application either because the efficiency of light emission of the obtained device is low.
Moreover, the above organic electric luminescence devices have a problem that the luminance of the light emission is decreased after the devices have been driven continuously for a long time, and this problem is another major obstacle for practical use of these devices.
In order to solve the above problems, a technology has been disclosed in which the generation of the leak current is prevented by using an amine of the dendrimer type, and the light emission can be maintained for a long time with stability (the specification of Japanese Patent Application Laid-Open No. Heisei 4(1992)-308688).
However, although this technology is effective for preventing the short-circuit, the stability of light emission is still insufficient for the practical application.
Accordingly, the present invention has an object of providing an organic electroluminescence device which has little possibility of dielectric breakdown after storage for a long time and shows a remarkably increased efficiency of light emission by using a material which is not easily crystallized as the hole injecting material, and an organic thin film which shows very excellent hole injecting and transporting properties and is advantageously used for the organic electroluminescence device and photosensitive films in the electronic photography.
The present invention has another object of providing a novel compound which provides an organic electroluminescence device having a long life and showing an excellent stability of light emission when the novel compound is used for the device.